Separation of comminuted cellulose acetate



Nov. 6, 1956 s. BIRD ErAL SEPARATION oF COMMINUTED cELLuLosE ACETATE Filed Jan. 5, 1954 FlG.

wsu/rais ,1T TRNE YS United States Patent() SEPARATION F COMMINUTED CELLULGSE ACETATE Stanley Bird and Albert Robinson, Spondon, near- Derby,

England, assgnors to British Celanese Limited, a corporation of Great Britain Application January 5, 1954, Serial No. 402,344

Claims priority,;application Great Britain January 6, 1953 s Claims.v (Cl. 209-235) in a mass of comminuted materials containing particles of both types.

According to the present invention, a method of separating particles of brous character from particles of granular character in a comminuted material containing both kinds of particles comprises causing the material to slide and roll unidirectionally down an oblique perforated surface, whereby the granular particles pass through the perforations in said surface while the fibrous particles remain supported thereby. The separation of the particles may be facilitated by periodically checking the descent of the material over the surface, by the provision of obstructions extending transversely to the direction of passage of the material over the surface; this appears to effect a moderate mixing or tumbling of the material during separation. The material treated is preferably already graded, before separation, to a size such that all its particles can pass through perforations similar to or somewhat smaller than those provided in the oblique surface employed.

By the procedure described above comminuted material consisting of a mixture of fibrous and granular particles can be separated into parts consisting substantially wholly of granular particles and substantially wholly of fibrous particles respectively, in a manner which is not possible by ordinary methods of screening. The method described above can most conveniently be carried out by means of an apparatus comprising a cylinder of wire mesh or perforated sheet material having its axisV slightly inclined to the horizontal with means for rotating said cylinder about said axis. The comminuted material to be separated is fed into the higher end of the cylinder and, as the cylinder rotates, Vis continually being lifted and allowed to roll or slide downwards towards the lowest generator of the cylinder, while slowly traversing the length of the cylinder from the higher to the lower Y end thereof. By choosing a cylinder of suitable dimensions, and a suitable speed of rotation, it can be arranged that, by the time the material remaining in the cylinder reaches the lower end thereof, it consists substantially wholly of fibrous particles, all the granular particles having left the cylinder through the meshes therein. A suitable collecting vessel is arranged beneath the cylinder to receive the granular particles, while the fibrous particles are discharged from the lower end of the cylinder into a separate vessel.

As a means for periodically checking the descent ofV the comminuted material across the inner surface of the cylinder, in order to facilitate the separation of the particles as indicated above, the cylinder may be provided with one or more deflector bars extending along the length of the inside of the cylinder close to the surface thereof, to check the passage of comminuted material across said surface as said cylinder rotates. To facilitate ff" 2,769,543 VvPatented Nov. 6, i956 the discharge of the fibrous material from the cylinder, oblique collector plates may be provided within the lower end of the cylinder to gather the fibrous material reaching the lower end of the cylinder, and to discharge it from the open end of the cylinder.

The invention is applicable generally to the separation of fibrous particles from granular particles but is particuiarly advantageous in the preparation of materials intended'for use in the method and apparatus described in U. S. application S. No1 243,994, filed August 28, 1951, in which powdered cellulose acetate or other fusible lament-forming material is supplied to one side of a heated plate having spinning orices therein so that the powdered material is fused by heat supplied through said plate, the fused .material being drawn away through said orifices in the form of lilaments. In this process the occurrence of particles of a fibrous character in the powdered material Vsupplied to theplate is aptto give rise to clogging of the apparatus employed and to other difficulties, and it is desirable that the vpowdered material employed should consist substantially wholly of particles of ak granular and not a fibrous character. The invention may also be regarded as particularly applicable to the treatment of cornrninuted cellulose acetate, a substance which is liable, from the mode of it's production to have a somewhat fibrous structure which persists to some degree through the grinding and comminuting of the material.

By way of example, one form of apparatus in accordance with the invention, and the manner in which it is used to carry out the method of the invention, will now be described in greater detail with reference to the accompanying drawings in which:

Figure 1 is a side elevation partly in section of the apparatus, and

Figure 2 is a section on the line 2-2 of Figure l, looking in the direction of the arrows.

The apparatus comprises a cylinder 4 made from 23 mesh copper gauze and having a length of about 4 and a diameter of about 14". The cylinder is supported internally on a pair of 4-armed spiders 5, one near each end. The spiders are mounted on a shaft 6 which is inclined at about 5 to the horizontal and s carried in bearings 7 lying outside the cylinder 4 at each end. The shaft 6 is driven at a speed of 3-4 revolutions per minute by means of a small electric motor 8 connected to the shaft by a belt 9 and pulleys 11.

Extending along the length of the cylinder 4 at a distance of about 1%" from the inner surface thereof are four bars 12, l in width and 1/4 in depth, each bar 12 being mounted, at each end, on an arm of one of the spiders 5. At the lower end of the cylinder 4 are two oblique collector plates 13 extending generally inwards from the wall of the cylinder 4, and meeting the wall along a line inclined at about 45 to the axis of the cylinder, the plates extending a little beyond the end of the cylinder 4 as well as for a short distance inside it, The shaft bearings 7 are mounted on the end members 14 of a suitable frame 15 which is also adapted to support beneath the cylinder 4 a trough 16 extending along the whole length of the cylinder. The cylinder is surrounded by a casing 17 carried by the frame 15 and having a slot-like opening at 18 immediately over the trough. Outside the lower end of the cylinder 4 is a chute 19 for guiding material discharged from the open end of the cylinder by the plates 13 into another trough or receiver 21 situated justY and which may contain from 10-15% by weightV of particles of brouscharacter. The screened'material is fed by chute 22 into the upper end of the cylinder 4 and, as the cylinder 4V rotates, is continually lifted and allowed to roll and slide down again towards the lowest generator Vof the cylinder. VThe four deector barsj12 inside the cylinder 4 periodically check the descentof the material and cause it to be slightly but not excessively tumbled and mixed. As the material passes slowly along the cylinder 4 from the upper to the lower end thereof, the granular particles drop through the meshes in the cylinder wall, and into the trough 16 lying beneath the cylinder. The fibrous material, however, continues to be supported by the inner wall of the cylinder 4 and reaches the lower end of the cylinder substantially free from granular particles. The ibrous particles are there gathered, as they roll down the inner wall of the cylinder 4 near the lower end thereof, by the collecting plates 13, and are discharged from the open end of the cylinder 4 into the Ychute 19 leading to the second trough 21.' p

In this way the material fed to the apparatus is divided into two parts, one consisting substantially Wholly of grancellulose acetate material containing both kinds of particles, said method comprising grading the material to a'size such that all its particles can pass through apertures of Va the material was graded, whereby the granular particles pass through said apertures while the brous particles remain supported thereby.

2. Method according Vto claim l comprising periodically-'- checking the descent of the graded material over they surface to effect a moderate tumbling of the material during separation. Y

ular particles and the other substantially wholly of fibrous particles.

Having described our invention, what we desire to secure by Letters Patent is: Y

1. A method of separating particles of fibrousV character from particles of granular character in a comminuted 3. Method according to claim 2 in which the comminuted cellulose acetate'gmaterial is iirst graded to a size such that it passes through a 52 mesh screen and said graded material contains l0 to 15% by weight of cellulose acetate particles of brous character, and in which the apertures of said oblique rotating 'surface are larger than those to which the material was graded.'

l References Cited in theiiile of this patent l UNITED STATES PATENTS Hamachek ,a v Dec. 9, 1941 

